This invention relates to crystal forms of azithromycin. Azithromycin is sold commercially and is an effective antibiotic in the treatment of a broad range of bacterial infections. The crystal forms of this invention are likewise useful as antibiotic agents in mammals, including man, as well as in fish and birds.
Azithromycin has the following structural formula: 
Azithromycin is described and claimed in U.S. Pat. Nos. 4,517,359 and 4,474,768. It is also known as 9-deoxo-9a-aza-9a-methyl-9a-homoerythomycin A.
Other patents or patent applications which directly or indirectly cover azithromycin include: EP 298,650 which claims azithromycin dihydrate; U.S. Pat. No. 4,963,531 which claims a method of treating a strain of Toxoplasma gondii species; U.S. Pat. No. 5,633,006 which claims a chewable tablet or liquid suspension pharmaceutical composition having reduced bitterness; U.S. Pat. No. 5,686,587 which claims an intermediate useful in the preparation of azithromycin; U.S. Pat. No. 5,605,889 which claims an oral dosage form that reduces the “food effect” associated with the administration of azithromycin; U.S. Pat. No. 6,068,859 which claims a controlled dosage form containing azithromycin; U.S. Pat. No. 5,498,699 which claims a composition containing azithromycin in combination with bivalent or trivalent metals; EP 925,789 which claims a method of treating eye infections; Chinese patent application CN 1123279A which relates to water soluble salts of azithromycin; Chinese patent application CN 1046945C which relates to azithromycin sodium dihydrogenphosphate double salts; Chinese patent application CN 1114960A which relates to azithromycin crystals, Chinese patent application CN 1161971A which relates to azithromycin crystals; Chinese patent application CN 1205338A which relates to a method of preparing water soluble salts of azithromycin; International Publication WO 00/32203 which relates to an ethanolate of azithromycin; and European patent application EP 984,020 which relates to an azithromycin monohydrate isopropanol clathrate.